The invention relates to a particle separator in an exhaust pipe of a diesel engine.
The term "fuel gases" as used herein after means in general hot gases having such a temperature that the burning of the particles separated in the separator is initiated in order to remove the particles for regenerating the filter means. These hot gases can be produced for instance by a combustion process using a burner unit or in any other way or even the exhaust gases of the engine can be directly used provided that the temperature thereof is appropriate for initiating the burning of the particles, such as carbon black particles in the exhaust gases of a diesel engine.
From German Offenlegungsschrift No. 32 04 176 a device is known for reduction of the particle emission of diesel engines by exhaust gas aftertreatment with a device having a particle separator-filter in an exhaust gas pipe of a diesel engine. Before the particle separator-filter inlet, a fuel gas line comes out into the exhaust gas pipe, by which fuel gases (gases that are the product of a burner combustion process for example), delivered by a burner, is fed to the particle separator-filter to regenerate it. With the help of a flap valve the exhaust gas in the exhaust gas pipe is deflected to a second particle separator-filter, when the first particle separator-filter is being regenerated and this flap valve then produces a flow connection with the fuel gas line and the intake side of the filter to be regenerated.
During normal operation of the particle separator-filter, when the flap valve shuts off the fuel gas line, it is observed, again and again, that exhaust gas leaks past the flap valve from the exhaust gas pipe and enters into the fuel gas line. It has been shown that a tight closing of such a flap valve, in the long run, cannot be brought about in an economically justifiable way. If exhaust gases from the exhaust gas pipe enter into the fuel gas line and get to the burner, as a result, the burner can be thermally overloaded and clogged so that reliable ignition and operation of the burner can no longer by guaranteed.
Accordingly, the present invention has a primary object of developing a particle separator within an exhaust gas pipe of a diesel engine which will, even with leaks present at the flap valve, shut off the fuel gas line, when the separator is not being regenerated, and no disadvantageous effect on the mode of operation of the burner is to be feared, if the burner is to be put into operation for regeneration of the separator.
According to preferred embodiments of the invention, a particle separator in an exhaust gas pipe of a diesel engine is provided which can be regenerated by means of fuel gases fed from a burner by a fuel gas line, in which a flap valve is placed between the intake side of the separator and the fuel gas line, which is opened for regeneration of the filter, and which significantly provides that the space in the fuel gas line between the flap valve and the burner is necessarily vented when the flap valve is closed.
With the design according to the invention, a particle separator in the exhaust gas pipe of a diesel engine is attained that, with the flap valve closed, exhaust gases going into the fuel gas line from the exhaust gas pipe are kept away from the burner. Especially if the flap valve does not tightly shut off the fuel gas line, these exhaust gases of the diesel engine are discharged before they reach the burner, thanks to the design according to the invention. Thus, the danger of a thermal overlaod of the burner and a clogging of it is effectively excluded.
According to a first preferred embodiment of the invention, a blower is installed upstream from the burner in the fuel gas line between the flap valve and the burner for venting of this space, a blower that constantly supplies air through the burner and through the space to be vented, when the flap valve in the fuel gas line is closed. The air supplied by the blower is then discharged into the environment by a vent pipe, which branches off from the first gas line before the flap valve. This blower may be an additional or auxiliary blower relative to the combustion air blower of the burner. The blower can suitably operate constantly, but at a reduced speed.
According to an alternate embodiment of the invention, a vent pipe branches off from the space of the fuel gas line to be vented, a vent pipe that contains a suction blower. The suction blower thus sucks gases from the space to be vented and delivers the withdrawn gases into the environment at its discharge side. To prevent functional impairments of the burner in its operating condition, when it is supposed to deliver fuel gases to the separator for regeneration, this venting pipe, or at least the blower, is preferably shut off during combustion operation of the burner.
Another alternate embodiment of the invention provides a bypass pipe, which goes from the space to be vented in the fuel gas line to a point in the exhaust gas pipe located downstream from the separator. In this connection, a negative pressure is produced in the bypass pipe, with the flap valve in the fuel gas line closed, a pressure that also prevails in the space to be vented, so that gases that have possibly come into this space are fed back into the exhaust gas pipe of the diesel engine by the bypass pipe and, thus, cannot get to the burner in the fuel gas line. To achieve this in the most constructive way possible, the portion of the bypass pipe that discharges into the exhaust gas pipe of the diesel engine downstream from the separator is so designed that this discharge portion operates as an injector or ejector which, on the basis of the flow conditions present in the exhaust gas pipe, independently produces a negative pressure in the bypass pipe.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only several embodiments in accordance with the present invention.